/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hive.ql.exec;

import java.lang.reflect.Method;
import java.util.List;

/**
 * The default UDF Method resolver. This resolver is used for resolving the UDF method that is to be
 * used for evaluation given the list of the argument types. The getEvalMethod goes through all the
 * evaluate methods and returns the one that matches the argument signature or is the closest match.
 * Closest match is defined as the one that requires the least number of arguments to be converted.
 * In case more than one matches are found, the method throws an ambiguous method exception.
 */
public class DefaultUDFMethodResolver implements UDFMethodResolver {

  /**
   * The class of the UDF.
   */
  private Class<? extends UDF> udfClass;
  
  /**
   * Constructor.
   * This constructor sets the resolver to be used for comparison operators.
   * See {@link UDFMethodResolver}
   */
  public DefaultUDFMethodResolver(Class<? extends UDF> udfClass) {
    this.udfClass = udfClass;
  }
  
  /**
   * Gets the evaluate method for the UDF given the parameter types.
   * 
   * @param argClasses The list of the argument types that need to matched with the evaluate
   *                   function signature.
   */
  public Method getEvalMethod(List<Class<?>> argClasses) 
    throws AmbiguousMethodException {
    Method m = FunctionRegistry.getMethodInternal(udfClass, "evaluate", false, argClasses);
    if (m == null) {
      throw new AmbiguousMethodException(udfClass, argClasses);
    }
    return m;
  }
}
